Spectral purity and reduced phase noise are becoming an inseparable requirement of signal generation and amplification circuits. Most modern communication systems, in particular, employ amplifiers that may be implemented as buffers and/or low-noise amplifiers (LNAs), for example, and are characterized with corresponding performance specifications. Those specifications normally dictate the performance of individual blocks, including voltage controlled oscillators (VCOs), dividers, etc. Traditionally, the noise and spectral profile of different blocks are included in a linear, phase domain AC-type analysis, or simulation, to estimate final spectral performance. Such analysis, however, ignores the nonlinear effects in the signal generation path, including an amplifying action by an amplifier, for example.
During operation of a conventional VCO, the VCO output is buffered before it is applied to the next stage. The buffer can be implemented as a power amplifier designed to deliver the signal to an off-chip load, or it may also be implemented as a simple tuned stage that sits between the VCO and a divider, for example. Because of the non-linear effect in the signal amplifier/buffer within an electric circuit containing a conventional VCO, for example, and the resulting phase noise profile, as outlined below, an amplifying action by an amplifier may substantially increase the phase noise profile of the generated signal at the output of the amplifier.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.